SUBSTITUTED RESORCINOL-BASED EPOXY RESINS

Abstract: A curable substituted resorcinol-based epoxy resin was developed having structural formula (I), wherein at least one of R1, R2 or R3 is selected from the group consisting of (a) hydrogen, (b) halogen, (c) a saturated hydrocarbon having 1 to 10 carbon atoms, (d) an unsaturated hydrocarbon having 1 to about 10 carbon atoms, (e) an aralkyl group, and (f) a benzoyl group. The aralkyl group has structure (II), wherein at least one of R4, R5 or R6 is selected from the group consisting of (a) hydrogen, (b) an alkyl group having 1 to about 4 carbon atoms and (c) halogen. The benzoyl group has structure (III), wherein R7 is selected from the group consisting of hydrogen, halogen and an alkyl group having 1 to 4 carbon atoms. Another curable substituted resorcinol-based epoxy resin was developed having general structural formula (IV), wherein at least one of R8, R9, R10 or R11 is selected from the group consisting of hydrogen, halogens and alkyl groups having 1 to about 10 carbon atoms. To minimize potential toxicity, the above derivatized resorcinol epoxies were synthesized, along with a series of thermoplastic tougheners. The physical and mechanical properties of the neat resins and of the toughened resins are presented in this patent.

Description: SUBSTITUTED RESORCINOL-BASED EPOXY RESINS This is a continuation-in-part of Application Serial No. 08/003,987, filed January 15, 1993, entitled "RESORCINOL-BASED EPOXY RESINS." 5 BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to substituted resorcinol- based epoxy resins having improved physical and mechanical properties such as a reduced ability to absorb moisture, 10 reduced toxicity, high glass transition temperature, good processability and less volatility. 2. Brief Description of the Prior Art Epoxy resins are a class of ther oset resins with a wide range of applications. For example, epoxy resins ar 15 employed in composite fabrication in both wet and dry lay-u techniques well known to those skilled in the art for the electrical, aerospace, filament winding and hardware indus¬ tries. The disadvantage of many epoxy resins is their ability to absorb high amounts of moisture when they are 20 used in both wet and dry composite fabrication. Obtaining an epoxy resin having a low moisture absorption characteris tic, however, in many cases, has led to a compromise in other desirable physical and mechanical properties such as, for example, high glass transition temperature, ease of > 25 processability, flexural properties, tensile properties and curing conditions. Epoxy resins are also used extensively in adhesiv formulations and matrix resins for advanced composites. Demanding applications such as modern advanced composites fabrications require materials with low viscosity for easier processing, relatively faster cure for minimizing processing costs in the fabrication of industrial goods and low toxicity to reduce worker risks from exposure during manufacturing operations. Once fabricated, it is necessary for the parts made using epoxy resins to exhibit good physical properties such as high glass transition temperature (Tg) and mechanical properties like flexural, tensile and fracture toughness properties to maximize parts life and minimize in-service failure. Although the epoxy resins provide the best attainable mechanical properties with carbon-fiber reinforced composite systems, higher levels of moisture absorption of these epoxy resins under hot/wet conditions deteriorate their properties. Therefore, epoxy resin producers are constantly developing new epoxy resins that can enhance physical and mechanical properties of both cured and uncured systems. Resorcinol diglycidyl ether (RDGE, unsubstituted) resin offers the unique advantages of having very low viscosity and high reactivity towards various curing agents. This low viscosity unsubstituted-resorcinol epoxy shows excellent cured physical and mechanical properties in advanced composites. But, unfortunately, this low viscosity resorcinol epoxy has been reported to cause skin cancer. The study of Kotin et al. (published in Cancer. vol. 9, p. 910, 1956 and Proceedings of the American Association for Cancer Research. Vol. 2, p. 229, 1957) on the carcinogenicity of 20 epoxy resins indicated that the unsubstituted resorcinol epoxy resin (RDGE) produced skin tumors in rats and mice. It is well known that all epoxy resins contain the epoxide, oxirane or ethoxylene group: \/V / wherein X represents the point of attachment to the remain¬ der of the resin molecule. The epoxide functionality generally appears in the form: known by those skilled in the art as the glycidyl group which is attached to the remainder of a compound by such as, for example, an oxygen (i.e., glycidyl ether), nitrogen (i.e., glycidyl amine) , or carboxyl group (i.e., glycidyl ester) . U.S. Patent No. 2,892,849 discloses a process for preparing epoxyalkyl aryl ethers, including resorcinol diglycidyl ether (RDGE) . U.S. Patent No. 4,916,202 discloses an epoxy resin having glycidyl amine groups. This patent discloses epoxy resins made from aliphatic amines, sulfonamides, and aromatic amines. Japanese Patent No. -026173 discloses a process for making an epoxy resin from a carboxylic acid derivative of resorcinol such as Beta-resorcylic acid. Lee and Neville in Handbook of Epoxy Resins. McGraw-Hill, 1967 and May and Tanaka in EPOXV Resins - Chemistry and Technology. Marcel-Dekker, 1973, have disclosed various kinds of epoxy resins, cured and uncured physical and mechanical properties with various curing agents and also products obtained from these resins. Japanese Patent No. -020172 discloses the process of making an epoxy resin from the reaction of another resorcinol derivative namely 4,4 , -thiodiresorcinol with epichlorohydrin. U.S. Patent No. 2,467,171 discloses stereoisomeri 1,3-diglycidyloxybenzenes (RDGE) which have been known for many years. Industrial and Engineering Chemistry. Volume 52, No. 4, April 1960, pp. 324-325 discloses epoxy resins from resorcinol-acetone condensation products. U.S. Patent No. 3,291,837 discloses the prepara- tion of monoepoxy compounds from benzoyl resorcinol and their application towards U.V. stabilizers. U.S. Patent No. 4,656,207 discloses resorcinol- based epoxy compounds but not benzoyl resorcinol diglycidyl ether compounds. None of the prior art discloses the preparation and application of diglycidyl ether derivatives of benzoyl resorcinol, styryl- and alphamethyl styryl substituted resorcinol, isopropyl substituted resorcinol and also the tetraglycidyl ether of bis[resorcinol] type resin of the present invention. In spite of these prior art disclosures, there remains a very real and substantial need for a resorcinol- based epoxy resin having lower toxicity, enhanced curing properties with various types of curing agents, good mechanical properties like flexural, tensile, and fracture toughness and physical properties like low moisture absorption, high glass transition temperature and low volatility. SUMMARY OF THE INVENTION The present invention has met the above-describe need. The present invention provides substituted resorcinol-based curable epoxy resin having the general structural formula (I) wherein at least one of R,, R_, or R 3 is selected from the group consisting of hydrogen, halogens, an alkyl group having 1 to about 10 carbon atoms, an alkene group having to about 10 carbon atoms, an aralkyl group and a benzoyl group. The aralkyl group has the following structure (II) wherein at least one of R 4 , R 5 or Re is selected from the group consisting of hydrogens, alkyl group having 1 to abo 4 carbon atoms, and halogens. The benzoyl group has the following structure (III) wherein R 7 is selected from the group consisting of hydrogens, halogens and alkyl groups having 1 to about 4 carbon atoms. In another embodiment of this invention, a curable epoxy resin is provided having the general structural formula (IV) wherein at least one of R 8 , ,, R, 0 or R n is selected from the group consisting of hydrogen, halogens and alkyl groups having 1 to about 10 carbon atoms. It is an object of this invention to develop new substituted-resorcinol based epoxy resins having reduced toxicity and reduced moisture absorption character while maintaining excellent cured physical and mechanical properties like the unsubstituted resorcinol epoxy. It is an object of the present invention to provide curable, substituted resorcinol-based epoxy resins having reduced toxicity, improved physical and mechanical properties including a substantially high glass transition temperature, a reduced moisture absorption capability, enhanced flexural, tensile properties with thermoplastic tougheners, and fracture toughness, and a substantially low viscosity. It is another object of this invention to provide a resorcinol-based epoxy resin that may be cured with con¬ ventional curing agents. It is another object of this invention, in view o the present environmental concerns of society, to make less volatile substituted resorcinol-based epoxy resin compounds that are characterized as less toxic compared to unsubstituted-resorcinol epoxy resins. It is a further object the present invention to provide less toxic substituted resorcinol-based epoxy resin having physical and mechanical properties equal to or bette than unsubstituted resorcinol epoxy resins which may be potential alternates in applications such as adhesive formulations and matrix resins for advanced composites. It is a further object of this invention to provide less toxic substituted resorcinol-based epoxy resin capable of enhancing the fracture toughness of a cured epox matrix, while maintaining the high flexural and tensile modulus like relatively highly toxic unsubstituted resorcinol epoxy resin. It is yet another object of the present invention to provide less toxic substituted resorcinol based epoxy resins that may be employed in the applications of coatings laminates, composites, adhesives, castings, molded and encapsulated articles. These and other objects of the invention will be more fully understood from the following description of the invention and the claims appended hereto. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is directed to improvement in the physical and mechanical properties such as, for example, the low moisture absorption capability, high glas transition temperature, tensile, flexural and fracture toughness properties, low volatility, high reactivity and low enough viscosity to reduce toxicity of these curable substituted-resorcinol based epoxy resins. As used herein, in the flexural and tensile data σ is a measure of strength, E is the modulus and e is elongation. K, c is the fracture strength or toughness and is the fracture energy. Tg is the glass transition temperature or softening temperature of the substituted epoxy resin of this invention. The curable epoxy resins of this invention have the following general structural formula (I) wherein at least one of R,, R 2 , or R 3 is selected from the group consisting of hydrogens, halogens, an alkyl group having 1 to 10 carbon atoms, an alkene group having 1 to 1 carbon atoms, an aralkyl group and a benzoyl group. The aralkyl group has the following structure (II) (I wherein at least one of R,, R s or R^ is selected from the group consisting of hydrogens, alkyl group having 1 to about 4 carbon atoms and halogens. The benzoyl group has the following structure (III) wherein R 7 is selected from the group consisting of hydrogens, halogens and alkyl groups having 1 to about 4 carbon atoms. In another embodiment of this invention, a curable epoxy resin is provided having the general structural formula (IV) wherein at least one of Rg, R,, R 10 or R„ is selected from the group consisting of hydrogen, halogens and alkyl groups having 1 to about 10 carbon atoms. The epoxy resins of the present invention can be cured in a conventional manner. Suitable hardeners for the epoxy resins of the present invention include dicyandiamide, aromatic amines such as diamino diphenylsulfone (hereinafter "DDS") which has the formula: and 4,4'-[l,4-phenylene(l-methylethylidene) ]-bis(2,6- dimethyl benzenamine) (Shell Development Company's curing agent 1062-M; hereinafter 1062-M) which has the following formula: and polycarboxylic acid anhydrides. The preferred curing agents are DDS and 1062-M. The amount of curing agent employed to cure the epoxy resins of the present invention will approximate the quantities employed with the presently used commercial resins such as EPON 828, EPON HPT 1071, EPON HPT 1072, EPON HPT 1079 and MY-720. Depending on the nature of the curing agent, curing can be performed at room temperature or at elevated temperatures. Curing provides a cross-linked polymer network which is infusible and intractable. It will be appreciated by those skilled in the art that cures normally involve an added accelerator such as, for example, benzyldimethylamine (BDMA) and boron trifluoride in the form of its monoethylamine, piperidine o methyli idazole complex. The epoxy resins of the present invention may also be mixed with conventional epoxy resins prior to curing. The epoxy resins of this invention can be toughened with functionally terminated acrylonitrile- butadiene copolymers, amine terminated propylene oxide oligomers, functionally terminated siloxane oligomers, and amine terminated thermoplastic tougheners such as polyethersulfone polymers. When amine terminated polyethersulfone was used as a toughener, the cured materi of the present invention showed considerable improvements i fracture toughness while retaining a high modulus and high glass transition temperature (Tg) . Suitable amine terminated polyethersulfones, that may be employed to enhance the toughness of the modified epoxy networks of th invention, preparations are disclosed in U.S. Patent No. 3,839,287 to Brode et al. and in McGrath et al.. Polymer. Vol. 30, p. 1552 (1989). It will be appreciated by those skilled in the a that while each commercially available epoxy resin has a number of advantageous properties, each resin, however, ha a shortcoming in that it substantially lacks at least one the hereinbefore mentioned properties generally required b those skilled in the art. By contrast, the epoxy resins o this invention generally have high glass transition temperatures, low water absorption properties, improved fracture toughness with amine terminated thermoplastic tougheners, less toxicity and improved flexural and tensil properties in comparison to the epoxy resin systems currently available. In this regard, the epoxy resins of this invention are well suited for most applications in which present commercial epoxy resins are employed includi surface coatings and the manufacture of composites for aircraft industry. Laminates made from the epoxy resin matrices of this invention include the use of fibers such as, for example, glass, polyaramide and carbon. It will be understood by those skilled in the art that the epoxy resin composites of this invention may be fabricated using conventional wet lay-up and dry lay-up methods. The reinforced fiber may be impregnated with the epoxy resin matrix to produce a prepreg sheet. The epoxy resins of thi invention are also suitable, for example, in the liquid for for filament winding, reaction injection molding, resin transfer molding and pultrusion. The epoxy resins of the present invention may be excellent adhesives, particularly for bonding metals to metals, composites to composites and metal to composites when formulated properly using methods which are well known to those skilled in the art. The epoxy resins of this invention are less volatile because of their bulky substituents and, therefore, less toxic as compared with other known unsubstituted resorcinol epoxy (RDGE) resins. The present invention is more fully illustrated b the following non-limiting examples: EXAMPLE 1 This example illustrates the preparation of the epoxy resin of this invention having the structure shown in formula (I) . Synthesis of Epoxy Resin from Benzoylresorcinol ΓRDGE-111 Benzoylresorcinol (240.8 grams; 1.125 moles) and epichlorohydrin (1041 grams; 11.25 moles) were placed in a 3-liter round bottomed flask fitted with a stirrer, thermom eter, Dean Stark condenser and an addition funnel. The contents of the flask were heated to about 100°-125° Centi¬ grade (C) and an aqueous sodium hydroxide solution (50% W/W 183 grams; 2.29 moles) was slowly added into the refluxing solution of benzoylresorcinol and the epichlorohydrin. While continuously removing the azeotropic water, the sepa¬ rated epichlorohydrin was continuously returned to the reaction flask. The addition time of sodium hydroxide was between about 1 to 1-1/2 hours and the time required for th complete removal of water (132 grams) was about 2 to 2-1/2 hours. After this, the excess epichlorohydrin was distille out first under atmospheric pressure and then under vacuum distillation conditions [maximum pot temperature about 130° 135°C and vacuum about 27-28 inches (") of mercury (Hg) ] . Then about 1200 ml of acetone was added to the reaction flask and the contents were refluxed for about 15 minutes t dissolve the epoxide. Finally, the salt, sodium chloride was filtered and the solvent acetone was distilled out usin both atmospheric and vacuum distillation conditions (temper ature about 95°-97°C and vacuum about 27-28" of Hg) to obtain 352 grams (yield = 96%) of epoxide having an epoxide equivalent weight (EEW) of 180. EXAMPLE 2 This example illustrates the epoxy resin of this invention having the structural formula (I) . Synthesis of Epoxy Resin from Benzoylresorcinol .RDGE-in Benzoylresorcinol (272.9 grams; 1.275 moles) and epichloro¬ hydrin (1180 grams; 12.75 moles) were placed in a 3-liter round bottomed flask fitted with a stirrer, thermometer, Dean Stark condenser and an additional funnel. The content of the flask were heated to about 100°-125°C and an aqueous sodium hydroxide solution (50% W/W; 207.4 grams; 2.59 moles was slowly added into the refluxing solution of benzoyl¬ resorcinol and epichlorohydrin. While continuously removin the azeotropic water, the separated epichlorohydrin was continuously returned to the reaction flask. The addition time of sodium hydroxide was between about 1 to 1-1/2 hours and the time required for the complete removal of water (149.6 grams) was about 2 to 2-1/2 hours. After this, the excess epichlorohydrin was distilled out first under atmospheric pressure and then vacuum distillation condition (maximum pot temperature about 130°-135°C and vacuum about 27-28" of Hg) . Then about 1300 ml of acetone was added to the reaction flask and the contents were refluxed for about 15 minutes to dissolve the epoxide. Finally, the salt, sodium chloride was filtered and the solvent acetone was distilled out using both atmospheric and vacuum distillatio conditions (temperature about 95°-97°C and vacuum about 27- 28" of Hg) to obtain 412 grams (yield = 99%) of epoxide having an epoxide equivalent weight of 194. EXAMPLE 3 This example illustrates the preparation of the epoxy resin of this invention having the structural formula (I). Synthesis of Epoxy Resin of Benzoylresorcinol fRDGE-III Benzoylresorcinol (272.9 grams; 1.275 moles) and epichloro¬ hydrin (1180 grams; 12.75 moles) were placed in a 3-liter round bottomed flask fitted with a stirrer, thermometer, Dean Stark condenser and an addition funnel. The contents of the flask were heated to about 100°-125°C and an aqueous sodium hydroxide solution (50% W/W; 214.5 grams; 2.68 moles was slowly added into the refluxing solution of benzoyl- resorcinol and epichlorohydrin. While continuously removin the azeotropic water, the separated epichlorohydrin was continuously returned to the reaction flask. The addition time of sodium hydroxide was between about 1 to 1-1/2 hours and the time required for the complete removal of water (153.2 grams) was about 2 to 2-1/2 hours. After this, the excess epichlorohydrin was distilled out first under atmos¬ pheric pressure and then vacuum distillation conditions (maximum pot temperature about 130°-135°C and vacuum about 27-28" of Hg) . Then about 1300 ml of acetone was added to the reaction flask and the contents were refluxed for about 15 minutes to dissolve the epoxide. Finally, the salt, sodium chloride was filtered and the solvent acetone was distilled out using both atmospheric and vacuum distillatio conditions (temperature about 95°-97°C and vacuum about 27- 28" of Hg) to obtain 402.5 grams (yield = 97%) of epoxide having an epoxide equivalent weight of 195. EXAMPLE 4 This example illustrates the epoxy resin of this invention having structural formula (I) . Synthesis of Epoxy Resin from Styryl-substituted Resorcino Preparation of Styrenated Resorcinol Into a 1-liter reaction flask equipped with a stirrer, ther mometer, reflux condenser and addition funnel, 165.0 grams of resorcinol were charged and heated to about 120°-130°C. para-Toluene sulfonic acid (1.0 gram) was then added at about 120°C and mixed for about 5 minutes. Then 234.5 gram of styrene (2.25 moles) were slowly added to the molten resorcinol dropwise over a period of about 1-1/2 hours. Th temperature of the reaction mixture was maintained between about 115°-135°C during the styrene addition. After all of the styrene had been added, the reaction mixture was stirre at about 115°-135°C for about an additional 1 to 1-1/2 hours. At the end of this period 0.5 grams of 50% W/W sodium hydroxide solution was added to neutralize the acid before cooling to room temperature. Structural characterization using infrared spectroscopy (IR) and nuclear magnetic resonance spectroscopy (NMR) of the above reaction product indicated the presence of 1.5 styryl group per resorcinol molecule. Analysis employing liquid chromatography (LC) and gas chromatography (GC) showed the presence of 1.4 weight percent unreacted resorcinol and als 0.01 weight percent unreacted styrene in the final product. Preparation of an Epoxy Resin from Styrenated Resorcinol ΓDGESRI Styryl resorcinol (359.0 grams; 1.35 moles) and epichlorohydrin (1249 grams; 13.5 moles) were placed in a 5-liter round bottomed flask fitted with a stirrer, thermometer. Dean Stark condenser and an additional funnel. The contents of the flask were heated to about 100°-125°C and an aqueous sodium hydroxide solution (50% W/W; 226.8 grams; 2.84 moles) was slowly added into the refluxing solution of styryl resorcinol and epichlorohydrin. While continuously removing the azeotropic water, the separated epichlorohydrin was continuously returned to the reaction flask. The addition time of sodium hydroxide was between about 1 to 1-1/2 hours and the time required for the complete removal of water (155 grams) was about 2 to 2-1/2 hours. After this, the excess epichlorohydrin was distille out first under atmospheric pressure and then vacuum distillation conditions (maximum pot temperature about 130° 135°C and vacuum about 27-28" of Hg) . Then about 1500 ml o acetone was added to the reaction flask and the contents were refluxed for about 15 minutes to dissolve the epoxide. Finally, the salt, sodium chloride was filtered and the solvent acetone was distilled out using both atmospheric an vacuum distillation conditions (temperature about 95°-97°c and vacuum about 27-28" of Hg) to obtain 514.5 grams of epoxide having an epoxide equivalent weight of 242. Structural characterization by IR/NMR analysis of the epoxide showed 1.83 epoxide groups per molecule. EXAMPLE 5 This example illustrates the epoxy resin of this invention having the structural formula (I) . Synthesis of Epoxy Resin from Styryl-substituted Resorcinol ΓDGEBRI Into a 1-litre reaction kettle fitted with a stirrer, ther¬ mometer. Dean Stark reflux condenser and an addition funnel 33.0 grams of resorcinol (0.3 moles) were placed. The kettle was then heated to melt the solid resorcinol. While maintaining the temperature of molten resorcinol between about 130° and 145°C, the catalyst p-toluenesulfonic acid (0.2 grams) was added first followed by the slow addition o 46.9 grams of styrene (0.45 moles) over a period of about 1/2 hour. After the styrene addition the reaction mixture was stirred at this temperature for about an additional 1.0 hour. Finally 0.2 grams of sodium hydroxide (50% W/W) was added to neutralize the acid catalyst. The styryl-substi- tuted resorcinol made was cooled to about room temperature before adding 227.5 grams of epichlorohydrin (3.0 moles). The contents of the kettle were again heated to about 100°- 125°C and an aqueous sodium hydroxide solution (50% W/W; 50.4 grams; 0.63 moles) was slowly added into the refluxing solution of styryl resorcinol and epichlorohydrin. While continuously removing the azeotropic water, the separated epichlorohydrin was continuously returned to the reaction flask. The addition time of sodium hydroxide was about 1 t 1-1/2 hours and the time required for the complete removal of water was about 2 to 2-1/2 hours. After this, the exces epichlorohydrin was distilled out first under atmospheric pressure and then vacuum distillation conditions (maximum pot temperature about 130°-135°C and vacuum about 27-28" of Hg) . Then, about 300 ml of acetone was added to the reac¬ tion flask and the contents were refluxed for about 15 minutes to dissolve the epoxide. Finally, the salt, sodium chloride was filtered and the solvent acetone was distilled out using both atmospheric and vacuum distillation condi¬ tions (temperature about 95°-97°C and vacuum about 27-28" o Hg) to obtain 104.3 grams of epoxide (yield = 92%) having a epoxide equivalent weight of 215. Structural characteriza- tion by IR/NMR analysis of the epoxide showed 1.97 epoxide groups per molecule. EXAMPLE 6 This example illustrates the epoxy resin of this invention having the structural formula (I) . Synthesis of Epoxy Resin from Alpha-Methylstyryl-substituted Resorcinol Preparation of Alpha-Methylstyryl Resorcinol Into a 3-litre kettle fitted with a stirrer, thermometer, reflux condenser and an addition funnel 137.5 grams of resorcinol (1.25 moles), 10.0 grams of oxalic acid, 900 ml of heptane were placed. The contents of the flask were the heated to about 65°C. While maintaining the temperature of the resorcinol slurry between about 65° and 75°C, 312 grams of alpha-methyl styrene (2.6 moles) was added dropwise with stirring for about 2.0 hours. After the completion of the above addition, the temperature of the reaction mixture was raised to and maintained at about 95°C and for an additiona period of about 2.0 hours while the reaction mixture was continuously stirred. The reaction mixture was cooled and the colorless product that separated was filtered, washed several times with distilled water and dried in air at abou room temperature to obtain 376 grams of alpha-methylstyryl- substituted resorcinol (yield = 84%) . Structural character ization by IR/NMR analysis of the above reaction product showed the presence of 1.85 alpha-methylstyryl groups per resorcinol molecule. Preparation of an Epoxy resin from Alpha-Methylstyrenated Resorcinol r pGE M SR 1 Alpha-methylstyryl resorcinol (65.6 grams; 0.2 moles) and epichlorohydrin (148 grams; 1.6 moles) were placed in a 500-ml round bottomed flask fitted with a stirrer, thermometer. Dean Stark condenser and an additional funnel. The contents of the flask were heated to about 100°-125°C and an aqueous sodium hydroxide solution (50% W/W; 36.8 grams; 0.46 moles) was slowly added into the refluxing solution of alpha-methylstyryl resorcinol and epichloro- hydrin. While continuously removing the azeotropic water, the separated epichlorohydrin was continuously returned to the reaction flask. The addition time of sodium hydroxide was about 1.0 hour and the time required for the complete removal of water (25.6 grams) was about 1-1/2 to 2 hours. After this, the excess epichlorohydrin was distilled out first under atmospheric pressure and then vacuum distillation conditions (maximum pot temperature about 130° 135°C and vacuum about 27-28" of Hg) . Then about 200 ml of acetone was added to the reaction flask and the contents were refluxed for about 15 minutes to dissolve the epoxide. Finally, the salt, sodium chloride was filtered and the solvent acetone was distilled out using both atmospheric an vacuum distillation conditions (temperature about 95°-97°C and vacuum about 27-28" of Hg) to obtain 88.0 grams of epoxide having an epoxide equivalent weight of 255. Structural characterization by IR/NMR analysis of the epoxide showed 1.94 epoxide groups per molecule. EXAMPLE 7 This example illustrates the epoxy resin of this invention having the structural formula (I) . Synthesis of Epoxy Resin from Isopropyl-Substituted Resorcinol Preparation of Isopropyl-Resorcinol A 3-neck, 2 1. flask equipped with a thermometer stirrer, Dean-Stark trap, addition funnel and condenser was charged with 550 g. (5 m.) of resorcinol, H 2 S0 4 (5 ml.) and 120 g. ( m.) of isopropyl alcohol. The flask was heated to reflux. Some alcohol was distilled off until the pot temperature reached 135°C. Alkylation appears to be faster at this temperature. Alcohol was added as needed to keep temperature between 135°C and 155 β C. Some lower boiling isopropyl ether was formed as a by-product and accumulated in the Dean-Stark which was then removed so as to maintain the reaction temperature. A total of 516 g. (8.6 m.) of isopropyl alcohol was added. A sample of the product after 12 hours showed less than 1% of unreacted resorcinol. NaOH (7.5 g.) pellets were added to the dark red thick liquid at 120°C to neutralize the sulfuric acid. Excess Na 2 C0 3 was added to ensure neutralization (C0 2 evaluation indicates acid still present) . The reaction product was distilled under vacuum a 130°C/10mm. to recover water and unreacted isopropyl alcohol. The isopropyl resorcinol was flask distilled at 165°C/4 mm. (pot temperature 175 β C) to a dry pot leaving a residue of inorganic water soluble salts. Weight of distilled product was 1032 g. The product was a mixture of 4-isopropyl resorcinol and 2,4-diisopropyl resorcinol. NMR and LC analysis showed that the final material contains 53 weight % of 4-isopropyl resorcinol and 47 weight % of 2,4- diisopropyl resorcinol. Preparation of Epoxy Resin from Isopropyl-Resorcinol .IPRDGE. Isopropyl-resorcinol (120.0 grams; 0.7 mole) and epichlorohydrin (583 grams; 6.3 moles) were placed in a 3- litres round bottomed flask fitted with a stirrer, thermometer, Dean-Stark condenser and an addition funnel. The contents of the flask were heated to about 100-125°C an an aqueous sodium hydroxide (50% w/w; 113.2 grams; 1.44 moles) was slowly added into the refluxing solution of isopropyl-resorcinol and epichlorohydrin. While continuously removing the ariotopic water, the separated epichlorohydrin was continuously returned to the reaction flask. The addition time of sodium hydroxide was about 1.0 to 1.5 hours and the time required for the complete removal of water (80.0 grams) was about 3.0 hours. After this, the excess epichlorohydrin was distilled out first under atmospheric pressure and then under vacuum distillation conditions (maximum pot temperature about 130-135°C and vacuum about 27-28" of Hg) . Then about 800 ml. of acetone was added to the reaction flask and the contents were refluxed for about 15 minutes to dissolve the epoxide. Finally, the salt, sodium chloride, was filtered and the acetone solvent was distilled out using both atmospheric an vacuum distillation conditions (temperature about 95-97°C and vacuum 27-28" of Hg) to obtain 189.3 grams of epoxide having an epoxide equivalent weight of 161 and viscosity 60 cps (Brookfield) . Structural characterization by IR/NMR analysis of the epoxide showed 1.82 epoxide groups per molecule. EXAMPLE 8 This example illustrates the epoxy resin of this invention having the structural formula (IV) . Synthesis of Epoxy Resin from 1,3-Bis [ ( 2,4-di-hvdroxyphenyl)-alpha-methyl ethyll benzene Preparation of 1,3-Bis [ (2,4-di-hydroxyphenyl)-alpha-methyl ethyll benzene Into a 2-litre kettle equipped with stirrer, thermometer, reflux condenser and an addition funnel, 264.0 grams of resorcinol (2.4 moles) 12.0 grams of oxalic acid and 900 ml of heptane were placed. The contents of this flask were heated to about 75°C. While maintaining the temperature of the resorcinolic slurry between about 75°-85°C, 126.4 grams of 1,3-diisopropenyl benzene (0.8 moles) was added dropwise for about 2 hours. After the completion of the above addi¬ tion, the temperature of the reaction mixture was raised to and maintained at about 95°C for about an additional 2.0 hours, while the reaction mixture was continuously stirred. The reaction mixture was then cooled and the separated heptane layer was removed by decantation. Finally the solidified mass was treated with excess dichloromethane to separate the reaction product. The white precipitate that separated from the solution was filtered, washed with dichloromethane and then washed with distilled water. Afte air drying at about room temperature the precipitate weighe 215 grams. Structural characterization by IR/NMR analysis of the reaction product confirmed the structure of 1,3- bis[ (2,4-di-hydroxyphenyl)-alpha-methyl ethyl] benzene. Preparation of an Epoxy Resin from 1,3-Bis [(2,4-di- hydroxyphenyl. -alpha-methyl ethyl] benzene 1,3-Bis [ (2,4-di-hydroxyphenyl)-alpha-methyl ethyl] benzene (15.1 grams; 0.04 moles) and epichlorohydrin (74.0 grams; 0.8 moles) were placed in a 500 ml round bottomed flask fitted with a stirrer, thermometer. Dean Stark condenser an an addition funnel. The contents of the flask were heated to about 100°-125°C and an aqueous sodium hydroxide solutio (50% W/W; 13.4 grams; 0.168 moles) was added slowly into th refluxing solution. While continuously removing the azeo- tropic water, the separated epichlorohydrin was continuousl returned to the reaction flask. The addition time of sodiu hydroxide was about 1.0 hour and the time required for the complete removal of water (9.6 grams) was about 1-1/2 to 2 hours. After this, the excess epichlorohydrin was distille out first under atmospheric pressure and then vacuum distillation conditions (maximum pot temperature about 140° 150°C and vacuum about 27-28" of Hg) . Then, about 130 ml o acetone was added to the reaction flask and the contents were refluxed for about 15 minutes to dissolve the epoxide. Lastly, sodium chloride was filtered out and the solvent acetone was distilled out using both atmospheric and vacuum distillation conditions (temperature about 95°-97°c and vacuum about 27-28" of Hg) to obtain 17.4 grams of a light yellow 1,3-bis [ (2,4-di-(2,3-epoxypropoxy) phenyl)-alpha- ethylethyl] benzene having an epoxy equivalent weight of 210. Structural characterization by IR/NMR of this epoxide showed 3.76 epoxide groups (Theory = 4.0) per molecule. Differential scanning calorimetry (DSC) analysis showed tha this resin had a softening point of 59.8°C. The epoxy resin prepared above was combined with the curing agent diaminodiphenyl sulfone (DDS) in a ratio o 10.0 grams of epoxy resin to 3.0 grams of DDS and cured to prepare a sample for the determination of glass transition temperature (Tg) . The cure cycle employed was about 2.0 hours at about 150°C followed by about 4.0 hours at about 200°C. The thermal mechanical analysis (TMA) measurements made on this cured epoxy resin showed a Tg of 244.7°C. Thi analysis was carried out in a nitrogen atmosphere at a heating rate of l0°C/minute. EXAMPLE 9 Synthesis of Amine Terminated Poly (arylene ether sulfone) oligomers Into a four necked round-bottomed flask fitted with a Dean- Stark trap, mechanical stirrer, thermometer and nitrogen inlet, bisphenol-A (11.41 grams; 0.05 mole), m-aminophenol (0.27 grams; 0.0025 mole), 4,4'-dichlorodiphenyl sulfone (14.72 grams; 0.051 mole), dried potassium carbonate (17.7 gram; 0.128 mole), N-methylpyrrolidone (160 ml.) and toluen (55 ml.) were added together. The reaction mixture was heated and taken to reflux and kept at this condition until all the water had been removed (approximately 4.0 hours). After this toluene was drawn from the Dean-Stark trap until the temperature increased to 155-160°C. The reaction was allowed to proceed for 8 hours, after which the solution wa cooled and filtered to remove the inorganic salts, then coagulated in an excess of rapidly stirred methanol-water mixture. The precipitate, which separated out, was filtere and washed several times with water and then methanol to completely remove all the salt and solvent. The precipitat was then dried at 80°C under vacuum to obtain m-aminophenol terminated polyethersulfone oligomer as a solid product. Structure of the resulting oligomers were confirmed by IR/NMR analysis. The number average molecular weight of the oligomers were determined by potentiometric titration of the endgroups. Differential Scanning Calorimetry (DSC) was used to determine the glass transitio temperature (Tg) of the oligomers. The two amine terminated polyethersulfone oligomers made from different molar ratios of bisphenol-A, dichlorodiphenyl sulfone and m-aminophenol (hereinafter Bisphenol-A Sulfone Toughener) had 3550 molecular weight (low; Tg = 125°C) and 13270 molecular weight (high; Tg = 162°C) EXAMPLE 10 Following Example 9, two amine terminated polyethersulfone oligomers were made using different molar ratios of resorcinol, dichlorodiphenyl sulfone and m- aminophenol reactants. These oligomers are hereinafter referred to as Resorcinol-Sulfone Toughener. The number average molecular weights of these two tougheners determine by titration are 3070 (low molecular weight) and 17860 (higher molecular weight) and had glass transition temperatures of 138°C (low) and 165°C (high) . EXAMPLE 11 Following Example 9, two amine terminated tougheners were synthesized using 4-benzoyl resorcinol, dichlorodiphenyl sulfone and m-aminophenol reactants. Thes oligomer tougheners are hereinafter referred to as Benzoylresorcinol-sulfone Toughener. The number average molecular weights and Tg of these tougheners were found to be 5460 (low; Tg 109°C) and 12429 (high; Tg 112°C) . These amine terminated polyethersulfone oligomers are used as tougheners to enhance the fracture toughness properties of the epoxy resins of the present invention. EXAMPLE 12 The following Table 1 sets forth the physical properties of the epoxy resins of Examples 1 through 6. Th viscosity was not measured for Examples 1 and 2. The viscosity for Example 3, however, determined at room temperature was found to be about 29 Pa's. It is important to note that this viscosity is higher than the unsubstituted-resorcinol epoxy resin (0.5 Pa*S; RDGE from Shell Development Company, Houston, Texas sold under the trade name of Heloxy 69) . Therefore, the epoxy resin (RDGE II) of the present invention is expected to be less toxic compared to RDGE due to lesser tendency to penetrate into the skin associated with higher viscosity. Also, it is important to note that the commercial epoxy resins presently available for higher performance composites and other applications have relatively higher viscosities compared to the resins of the present invention Therefore, the epoxy resin of this invention has a processing advantage over the present commercial epoxy resins. Because the resin of this invention has such a low viscosity, it will be understood by those skilled in the ar that it is suitable for more automated manufacturing processes such as, for example, resin transfer molding, reaction injection molding and pultrusion. Table 1 Synthesis and Physical properties of Diglycidyl ether of Benzoyl resorcinol (RDGE-II) 3 99 97 194 195 0.39 0.4 29 0.2 0.7 0.04 o. l From the IR/NMR analysis it was found out that RDGE-II possess greater than 1.9 epoxy groups per molecule; thereby expected to show higher reactivity towards differen curing agents. EXAMPLE 13 o study the neat resin mechanical properties of the substituted resorcinol epoxy resins of the present invention, the epoxy resins were blended with the curing agents like diaminodiphenyl sulfone (DDS) and Shell's 1062- curing agents at about 130-140°C and void-free castings wer made from the molten resin blend using silicone molds. The flexural specimens were measured 76.2 mm x 12.7 mm x 3.3 mm. Tensile dogbone specimens measured 152.4 mm x 12.7 mm x 3.3 mm with a 5.1 mm wide gage section. The mode I fracture toughness specimens measured 152.4 mm x 15. mm x 3.3 mm. Three 5 mm notches were cut into the specimens two inches apart, and a sharp razor blade was used to precrack them before fracture testing. The standard epoxy resin cure cycle (cure a') was 2.0 hours at 150°C, followed by 4.0 hours at 200°C. Anothe cure cycle (cure x b'), used solely for comparison of DDS an 1 062-M in the unmodified resin, was 2.0 hours at 180°C followed by 2.0 hours at 210°C. These curing cycles are referred to as x cure a' and Λ cure b' respectively. Summaries of the test results for the cured RDGE- II resins of this invention are shown in Table 2. Table 2. Neat Resin Properties of RDGE-II Cured with DDS and 1062-M at Different Cure Conditions Cum Cycle Flexural σ(MPa) E GPaJ ε(%) Tensile σ(MPa) E (GPa) « (%) G«(JAn z ) Moisture pckup (%) T«( β Q Mechanical properties like flexural and tensile properties are observed to be higher and the moisture picku was found to be about 2.8 weight percent for DDS cured resins and about 1.4 weight percent for 1062-M cured resins after 48 hours of water boil. The fracture toughness (K [C and G IC ) values indicate that these systems have to be toughened in order to use as matrix resins for tough composite parts fabrication. EXAMPLE 14 The mechanical properties of RDGE-II cured with DDS at different cure conditions are given in Table 3 hereinafter. High flexural strength and modulus are maintained irrespective of the cure conditions. In additio to mechanical properties, the Tg does not change significantly, indicating that this resin system is very forgiving of varying cure conditions. Table 3. Neat Resin Properties of RDGE-II Cured with DDS at Different Cure Conditions RDGE-II : lOO DDS: 35-36 g Cure cycle (h °C) 2/180 4 150 2/150 1/150 Postcure 2/210 7/200 4/200 3/225 Property Flexural Strength (MPa) 184.1 169.6 Modulus (GPa) 4.2 4.3 Elongation (%) 6.5 4.7 Glass Transition 171.0 166.0 175.0 175.5 Temperature (T g by TMA, °C) Moisture absorption 3.0 ND 3.1 3.0 (%, after 48 hours water boil) Impact Strength 0.5 ND 0.38 0.4 (Notched Izod; ft.-lb/in) = Not Determined EXAMPLE 15 The flexural measurements results on RDGE-II cure with DDS at elevated temperatures are given in Table 4 hereinbelow. As can be expected, both the flexural strengt and modulus decreased as the temperature increased. At 121°C, 57% of the room temperature flexural strength and 50 of flexural modulus were retained, which is similar to the performance of other high performance epoxy resins. Table 4. Elevated Temperature Mechanical Properties of RDGE-II Cured with DD Resin/Curing Agent: RDGE: 100.0 g DDS: 35-36g Cure Cycle (h/°C) 2/150 Postcure 4/200 Temperature( β O 25 65.5 121.1 Flexural Property Strength (MPa) 186.4 158.6 106.9 Modulus (GPa) 4.5 3.3 2.3 Elongation (%) 4.6 6.9 5.9 EXAMPLE 16 Flexural properties obtained after 48 hours water boil on the RDGE-II/DDS cured samples are presented in Tabl 5 hereinafter. From the results of the experiments, it was found that RDGE-II retains about 80% of its strength and 86- 95% of its modulus even after water boil. Table 5. Neat Resin Properties of RDGE-II Cured with DDS and after Water Boil * EXAMPLE 17 The neat resin mechanical properties of RDGE-II and RDGE resins obtained are given in Table 6 hereinbelow. The curing agent used was DDS and both 'cure a' and 'cure b conditions were used. Table6. Neat Resin Properties of RDGEand RDGE-II Cured with DDS From the results of the flexural and tensile data, it is very clear that the performance of RDGE-II is similar to RDGE. The Tg of RDGE-II is about 10 β C lower than RDGE. This lower Tg value is due to the substitution on the benzene ring which results in a reduction in the crosslink density. Another important result of the benzene ring substitution which leads to an improvement of RDGE-II over RDGE can be seen from the moisture pickup values. RDGE-II absorbs about 2.8% water compared to 3.6% for RDGE in the 4 hour water boil test. It is expected that this would translate into an improved elevated temperature performance of RDGE-II compared to RDGE. EXAMPLE 18 The following table (Table 7) shows the compariso of the mechanical properties of the present invention to that of the commercial resins. Table 7. Neat Resin Mechanical properties Comparison Epoxy Resin = 100 g Resin RDGE-II ARALDITE DER 332 XU MY 722 Curing Agent (g) 35.0 50.0 33.0 (DDS) Cure Cycle, 2/180 2/150 2/180 2/150 Hours,/°C 2/210 4/200 2/210 4/200 Flexural Properties (Dry) Strength (MPa) 173.7 186.2 125.7 125.7 Modulus (GPa) 4.4 4.3 4.1 3.0 Strain (%) 5.4 6.2 5.4 Moisture Absorption (%) 3.0 3.7 (After 48 hours water boil) Table 7 shows the mechanical properties of cured Araldite XU MY 722 taken at 25°C and DER 332. Araldite XU MY 722 is commercially available from Ciba-Geigy Corporation, Hawthorne, New York, U.S.A. and DER 332 is commercially available from Dow Chemical, U.S.A. Araldite was cured with aromatic diamine hardener HT 976 (DDS) commercially available from Ciba-Geigy Corporation. Table shows that the cured resin of this invention (RDGE-II) and the cured Araldite resin and DER 332 were cured under a two step cure cycle. From the results of the above table, it will be appreciated that the epoxy resin of this invention has improved flexural properties as compared to Araldite an DER 332. Further, another advantage of the epoxy resin of RDGE-II is that it has 3% moisture absorption after 48 hour of being boiled in water. In contrast, Araldite has a 3.7% moisture absorption. EXAMPLE 19 Neat resin castings of cured epoxy materials containing both an amine terminated polyarylether sulfone oligomers (Examples 9, 10 and 11) and curing agent were don as follows using high and low molecular weight tougheners. The toughener employed in the resin castings were 5, 10 and 15 weight percent of the final cured material. The epoxy resin was first mixed with the toughener at 120-135°C. The mixing times varied depending on the epoxy resin and on the toughener level. For example, when using RDGE-II and the bisphenol-A based toughener, complete mixing was accomplished after 2 hours at 120°C, while for RDGE, the mixing times could be as short as 15 minutes. After the toughener had formed a homogeneous solutions with the epox a stoichiometric amount of DDS was added to the mixture and stirre d at 1 30°C until it dissolved. The solution was the degassed under vacuum for 15 minutes. The RDGE-II resins with high loadings of toughener were vented to atmospheric pressure an d degassed for several cycles in order to remove all the entrained air. After degassing, the resin was poured into preheated silicone molds and cured using 'cure a' conditions. EXAMPLE 20 N eat resin properties of RDGE-II and RDGE cured with DD S an d amine terminated reactive bisphenol-A sulfone toughener are present in Tables 8 and 9 hereinbelow. Table8. Effectof Bisphenol-ASulfoneTougheneron RDGE-II Mechanical and Physical Properties Table 9. Effectof Bisphenol-A SulfoneTougheneron RDGE Mechanical and Physical Properties From the results of toughening experiments, the modulus of RDGE-II and RDGE remained essentially unchanged. This thermoplastic toughener had the most positive overall effect on RDGE-II compared to RDGE. In the case of RDGE-II fracture energy increased from 69.1 J/m 2 in the unmodified resin to 269 J/m 2 with 15% of the higher molecular weight toughener. The fracture toughness increased almost 4 times but the Tg was maintained. With RDGE, the fracture toughness increased by 18% and Tg decreased by 20°C. These results indicated that the thermoplastic modified RDGE-II has a higher TG, higher modulus, lower moisture absorption (by almost 50%) and toughness properties comparable to RDGE EXAMPLE 21 Neat resin properties of RDGE-II and RDGE cured with DDS and amine terminated reactive resorcinol sulfone toughener are presented in Tables 10 and 11 hereinbelow. Table 10. Effect of Resorcinol-Sulfone Toughener on RDGE-II Mechanical and Physical Properties Table 11. Effect of Resorcinol-Sulfone Toughener on RDGE Mechanical and Physical Properties Toughen level Flexural σ(MPa) E (GPa) ε(%) Tensile σ(MPa) E .? f> κ Mgo£isWture pickup (%) Tg( β O From the results of Tables 10 and 11, the resorcinol sulfone enhances the fracture energy of RDGE-II higher than that of RDGE where the toughener provides virtually no improvement. The resorcinol toughener also improves the lower moisture absorption characteristics of RDGE -II compared to RDGE resin. EXAMPLE 22 Neat resin properties of RDGE-II and RDGE cured with DD S and amine terminated reactive benzoyl resorcinol sulfone toughener are shown in Tables 12 and 13 hereinbelow. Table 12. Effect of Benzoyl resorcinol-Sulfone Toughener on RDGE-II Mechanical and Physical Properties Table 13. Effect of Benzoyl resorcinol-Sulfone Toughener on RDGE Mechanica and Physical Properties With benzoyl resorcinol sulfone toughener the flexural modulus of both RDGE-II and RDGE resins are maintained. Also, there is an improvement in fracture toughness and fracture energy in both RDGE-II and RDGE but the moisture pickup is unchanged from the neat resin without any added toughener. EXAMPLE 23 Table 14 shows the mechanical properties of diglycidylether of styrylresorcinol (DGESR) of Example 4 that has been cured with DDS. Table 14 hereinbelow shows that the epoxy resin had a very high flexural modulus of 4.7 mPa but had a low glass transition temperature of 128.8°C. Table 14. Mechanical properties of DGESR Cured with DDS DGESR, g. (From Example 4) 100 DDS, g. 27.5 Flexural Properties (Dry) Strength (MPa) 129.0 Modulus (GPa) 4.7 Elongation (%) 2.8 Cure Cycle, HoursAC (1) 23/120 (2) 4/175 Glass Transition Temperature, °C (TMA) Dry 128.8 EXAMPLE 24 Table 15 hereinbelow shows the mechanical properties of diglycidylether of alphamethylstyrylresorcinol (DGEMSR) of Example 6 that has been cured with DDS. Table 15 shows that the epoxy resin had an acceptable glass transition temperature of 164.8°C and had acceptable flexural properties. The epoxy resin had a 2% moisture absorption after 48 hours of water boil. It will be appreciated, therefore, that the epoxy resin has a very low moisture absorption ability. This property is particularly advantageous for a resin employed in an environment having high humidity level. Table 15. Mechanical Properties of DGEMSR Cured with DDS DGEMSR, g. (From Example 6) 100 DDS, g. 20.5 Flexural Properties (Dry) Strength (MPa) 88.0 Modulus (GPa) 3.7 Elongation (%) 2.4 Flexural Properties (Wet) (After 48-hours water boil) Strength (MPa) 52.5 Modulus (GPa) 3.8 Elongation (%) 1.1 Cure Cycle, HoursΛC (1) 2/120 (2) 4/200 Glass Transition Temperature, °C (TMA) Dry 164.8 Moisture Absorption (%) (After 48-hours water boil) 2.0 Impact Strength (Ft-lb/in) 0.48 (Notched Izod) EXAMPLE 25 Table 16, below, shows the neat resin mechanical properties of isopropyl-substituted resorcinol epoxy resin of Example 7 and the effect of 30% bisphenol-A sulfone toughener on the cured resin properties. Table 16. Isopropyl-resorcinol epoxy Properties Cured with stoichiometric amounts of DDS 30% Bisphenol-A/sulfone touσh ( 13270 M.W.) 2 hr/150°C 4 hr/200°C 122.7 3.3 4.2 61.4 3.1 3.1 0.67 117.0 From Table 16, the toughener maintains the flexural and tensile modulus of neat resin. The fracture toughness and energy of this isopropyl-resorcinol epoxy was slightly and not significantly improved by the addition of the toughener. But the glass transition temperature (Tg) was not affected much by the presence of the sulfone toughener. EXAMPLE 26 Example 8 sets forth the preparation of an epoxy resin of this invention that may be made from l,3-bis[2,4- di-hydroxyphenyl)-alpha-methyl-ethyl] benzene. The resulting epoxy resin of Example 8 was cured for about 2 hours at about 150°C and then for about 4 hours at about 200°C. Thermal mechanical analysis measurements showed a glass transition temperature for this epoxy resin of 244.7°C. Accordingly, it will be appreciated that the epox resin of Example 8 had a glass transition temperature greater than the glass transition temperature of the epoxy resins of Examples 1 through 7. EXAMPLE 27 Table 17, below, shows the results of toxicity studies of both RDGE and RDGE-II as an eye irritant and dermal irritant on mice and rats. Table 17 EDGE RPGE-π dermal irritant (a) well-defined redness (a) slight degree of redness and swelling at one hour and barely perceptible swelling at one hour (b) no appreciable (b) complete recovery at 24 hours recovery over the 72-hour observation period eye irritant (a) a severe degree of (a) light irritation to the conjuncti irritation involving the but not the cornea or iris cornea and deeper tissue (b) no recovery at 72 hours (b) full recovery at 48 hours The data set forth hereinbefore and Table 18, hereinafter, which summarizes the results from the substituted resorcinol-based resins, clearly demonstrate that the epoxy resins of this invention have improved mechanical and physical properties over the presently commercially available epoxy resins. Ε-t-le lβ Summary of Remits from Substituted Resorcinol Bated Resins Epoxy Ha tin RDGE RDGE-II IPRDGE DGESR DGEMS (Example 2) (Example 7) (Example 5) (Exampl U BCTrPti PϊTOBtt 1. Epoxy eq.weight 130 180-195 161 215 255 2. Visoostty (Fa*.2-5 * Q 0.5 25.0-30.0 0.6 60.0 N.D. 3. Epoxy groups per molecule >1.9 1.9-l.ftS 1.82 1.97 1.94 1. Curing Agent Used* DDS DD6 DDS DDS DDS 2. Cuιecyde(-_rC) 2/150 Postcurc 4200 3. Flexural Swag* (MPa) 133.1 Modulus (GPa) 3.2 Elongation (%) 4.9 4.T, C) 182.0 173.0 179.1 128.8 165.0 * a. Stotchiometric amount used. N-D. * Not determined. Moisture Absorption (%) after 48 hours water boil 3.5Θ 3.0 N.D. N.D. 2.0 Whereas particular embodiments of this invention have been described above for purposes of illustration, it will be evident to those persons skilled in the art that numerous variations of the details of the present invention may be made without departing from the invention as defined in the appended claims.

Claims: WE CLAIM: 1. A curable substituted resorcinol-based epoxy resin having the structural formula: wherein at least one of R,, R, or R 3 is selected from the group consisting of (a) hydrogen, (b) halogen, (c) a saturated hydrocarbon having 1 to about 10 carbon atoms, (d) an unsaturated hydrocarbon having 1 to about 10 carbon atoms, (e) an aralkyl group and (f) a benzoyl group. 2. The substituted resorcinol-based epoxy resin of Claim 1, wherein the aralkyl group has the following structure: 1 R 4 -C-R s , wherein at least one of R,, R 5 or R,-. is selected from the group consisting of (a) hydrogen, (b) an alkyl group having 1 to about 4 carbon atoms and (c) halogen. 3. The substituted resorcinol-based epoxy resin of Claim 1, wherein the benzoyl group has the following structure: wherein R 7 is selected from the group consisting of (a) hydrogen, (b) halogen, and (c) an alkyl group having 1 to 4 carbon atoms. 4. The curable substituted resorcinol-based epoxy resin of Claim 1, wherein said epoxy resin before being cured is characterized by being substantially topically non-toxic to human beings. 5. The curable substituted resorcinol-based epoxy resin of Claim 1, wherein said epoxy resin is characterized by having reduced moisture absorption properties after being cured. 6. The curable substituted resorcinol-based epoxy resin of Claim 1, wherein said epoxy resin is characterized by having a high glass transition temperature after being cured. 7. The curable substituted resorcinol-based epoxy resin of Claim 1, wherein said epoxy resin before being cured is characterized by being less volatile compared to unsubstituted resorcinol-based epoxy resins. 8. The curable substituted resorcinol-based epoxy resin of Claim 1, wherein said epoxy resin before being cured is characterized by having a viscosity high enough to effect reduction of topical resin toxicity. 9. The curable substituted resorcinol-based epoxy resin of Claim 1, including said epoxy resin having a toughener agent therein whereby said epoxy resin is characterized by maintaining flexural properties and tensile properties after being cured. 10. The curable substituted resorcinol-based epoxy resin of Claim 9, wherein the K IC -fracture toughness and G IC -fracture energy are higher with tougheners than such properties in the untoughened substituted resorcinol-based epoxy resins. 11. The curable substituted resorcinol-based epoxy resin of Claim 9, employing said substituted resorcinol-based epoxy resin as an adhesive to bond metal t metal, metal to composites and composite to composite. 12. The curable substituted resorcinol-based epoxy resin of Claim 9, employing said substituted resorcinol-based epoxy resin in coating formulations. 13. The curable substituted resorcinol-based epoxy resin of Claim 9 , wherein the tougheners are about 1% to 15% by weight. 14. A tough, durable composite part comprising: a matrix resin, tougheners and filler materials; said matrix resin being comprised of a curable substituted resorcinol-based epoxy resin having the structural formula: wherein at least one of R,, R-j or R 3 is selected from the group consisting of (a) hydrogen, (b) halogen, (c) a saturated hydrocarbon having 1 to about 10 carbon atoms, (d an unsaturated hydrocarbon having 1 to about 10 carbon atoms, (e) an aralkyl group and (f) a benzoyl group. 15. The composite part of Claim 14, wherein said composite part is characterized by maintaining flexural properties and tensile properties after being cured. 16. The composite part of Claim 14, wherein said composite part is characterized by maintaining a high glass transition temperature. 17. The composite part of Claim 14, wherein said composite part is characterized by having reduced moisture absorption properties. 18. A curable substituted resorcinol-based epoxy resin having the general structural formula: wherein at least one of R 8 , R,, R 10 or R n is selected from th group consisting of hydrogen, halogens and alkyl groups having 1 to about 10 carbon atoms. 19. The curable substituted resorcinol-based epoxy resin of Claim 18, wherein said epoxy resin after being cured is characterized by having a higher glass transition temperature than the unsubstituted resorcinol- based epoxy resins. 20. The curable substituted resorcinol-based epoxy resin of Claim 18, wherein said substituted resorcinol-based epoxy resin is used as an adhesive to bond metal to metal, metal to composites and composite to composite. 21. The curable substituted resorcinol-based epoxy resin of Claim 18, wherein said substituted resorcinol-based epoxy resin is used in coating formulations. 22. A tough, durable composite part comprising: a matrix resin, tougheners and filler material; said matrix resin being comprised of a curable substituted resorcinol-based epoxy resin having the general structural formula: wherein at least one of R 8 , R,, R 10 or R n is selected from th group consisting of hydrogen, halogens and alkyl groups having 1 to about 10 carbon atoms. 23. The tough, durable composite part of Claim 22, wherein said composite part is characterized by maintaining flexural properties and tensile properties afte being cured. 24. The tough, durable composite part of Claim 22, wherein said composite part after being cured is characterized by having a higher glass transition temperature than the unsubstituted resorcinol-based epoxy resin composite part.

Inventors: DURAIRAJ RAJ B, TACKIE MICHAEL N, DURAIRAJ, RAJ, B., TACKIE, MICHAEL, N.
Applicants: DURAIRAJ RAJ B, INDSPEC CHEMICAL CORP, TACKIE MICHAEL N, DURAIRAJ, RAJ, B., INDSPEC CHEMICAL CORPORATION, TACKIE, MICHAEL, N.
Application year: 1994
Main classification: C08G59
IPC codes: C07D303, C08G59